1. Field of the Invention
The present invention relates to subterranean fluid lines. More specifically, the invention relates sewage systems. More particularly still, the invention relates to improved methods and apparatus for isolating a section of a fluid line.
2. Description of the Related Art
Pumping stations in sewage collection systems, also called lift stations, are normally designed to handle raw sewage that is fed from underground gravity pipelines (pipes that are laid at an angle so that a liquid can flow in one direction under gravity). Sewage is fed into and stored in an underground pit, commonly known as a wet well. The well is equipped with electrical instrumentation to detect the level of sewage present. When the sewage level rises to a predetermined point, a pump or pumps will be started to lift the sewage upward through a pressurized pipe system from where the sewage is discharged into a gravity manhole. From there, the cycle starts all over again until the sewage reaches its point of destination—usually a treatment plant. By this method, pumping stations are used to move waste to higher elevations.
Sewage pumping stations are typically designed so that one pump or one set of pumps will handle normal peak flow conditions. Redundancy is built into the system so that in the event any one pump is out of service, the remaining pump or pumps will handle the designed flow. There are a lot of electronic controllers designed specially for this application. The storage volume of the wet well between the ‘pump on’ and ‘pump off’ settings is designed to minimize pump starts and stops, but is not so long a retention time as to allow the sewage in the wet well to overflow. In the case of high sewage flows into the well (for example during peak flow periods and in system also handling rain water), additional pumps will be used. If this is insufficient, or in the case of failure of the pumping station, a backup in the sewer system can occur leading to a sanitary sewer overflow—the discharge of raw sewage into the environment.
Pump stations and/or sections of sewer lines are taken off-line for a variety of reasons including equipment failure and/or maintenance. Breakdown due to corrosion is typical. Sewage infrastructure corrosion occurs when sewage gas (H2S) is converted to sulfuric acid (H2SO4) by the action of bacteria. Currently, the stations are taken off-line using methods that are time-consuming, difficult and dangerous. For example, in one method an inflatable pig-like device is inserted in the sewer via a manhole at some location upstream of the trouble zone. Thereafter, the pig is inflated in order to expand and block the flow of fluid. At the same time, the fluid is re-routed at a location downstream of the pig. Isolating a section of sewer in this manner is effective, but working downstream of an inflated pig is inherently dangerous in the event of deflation or rupture of the pig, which can result in a renewed flow of fluid in the direction of workers in the sewer who may not have an avenue for safe exit. In other instances, lift stations at water treatment facilitates fail and the resulting repairs on pumps is inefficient due to the presence of temporary pumps and flow lines in and around the facility.
What is needed is an efficient and safe way to isolate one section of a sewer from another section or from a lift or treatment facility.